The role of beta-gamma oscillations in unexpected rewards processing.

Reward processing in humans is carried out by an extensive fronto-subcortical network that might be coordinated by fast oscillatory electrical activity. Previous studies have identified an increase in beta-gamma oscillatory activity after the processing of positive feedback stimuli but the functional role of this electroencephalographic (EEG) correlate remains unclear. In the present study, we used event-related brain potentials (ERPs) and trial-by-trial wavelet-based time-frequency analysis of the EEG signal to investigate the effects of expectancy and magnitude of positive and negative feedbacks associated with monetary gains and losses in a gambling task. Large increase of beta-gamma oscillatory activity only in unexpected monetary gains was observed,irrespective of its magnitude. Based on recent findings we propose that this increase in beta-gamma oscillatory activity might reflect a general cognitive mechanism in charge of monitoring unexpected positive events based on feedback processing.